Black Box Explains...T1 and E1

If you manage a heavy-traffic data network and demand high bandwidth for high speeds, you need digital super-fast T1 or E1.

Both T1 and E1 are foundations of global communications. Developed more than 35 years ago and commercially available since 1983, T1 and E1 go virtually anywhere phone lines go, but they’re much faster. T1, used primarily in the U.S., sends data up to 1.544 Mbps; E1, used primarily in Europe, supports speeds to 2.048 Mbps. No matter where you need to connect—North, South, or Central America, Europe, or the Pacific Rim—T1 and E1 can get your data there fast!

T1 and E1 are versatile, too. Drive a private, point-to-point line; provide corporate access to the Internet; enable inbound access to your Web Server—even support a voice/data/fax/video WAN that extends halfway around the world! T1 and E1 are typically used for:
• Accessing public Frame Relay networks or Public Switched Telephone Networks (PSTNs) for voice or fax.
• Merging voice and data traffic. A single T1 or E1 line can support voice and data simultaneously.
• Making super-fast LAN connections. Today’s faster Ethernet speeds require the very high throughput provided by one or more T1 or E1 lines.
• Sending bandwidth-intensive data such as CAD/CAM, MRI, CAT-scan images, and other large files.

Scaling T1
Basic T1 service supplies a bandwidth of 1.536 Mbps. However, many of today’s applications demand much more bandwidth. Or perhaps you only need a portion of the 1.536 Mbps that T1 supplies. One of T1’s best features is that it can be scaled up or down to provide just the right amount of bandwidth for any application.

A T1 channel consists of 24 64-kbps DS0 (Digital Signal [Zero]) subchannels that combine to provide 1.536 Mbps throughput. Because they enable you to combine T1 lines or to use only part of a T1, DS0s make T1 a very flexible standard.

If you don’t need 1.536 Mbps, your T1 service provider can rent you a portion of a T1 line, called Fractional T1. For instance, you can contract for half a T1 line—768 kbps—and get the use of DS0s 1–12. The service provider is then free to sell DS0s 13–24 to another customer.

If you require more than 1.536 Mbps, two or more T1 lines can be combined to provide very-high-speed throughput. The next step up from T1 is T1C; it offers two T1 lines multiplexed together for a total throughput of 3.152 on 48 DS0s. Or consider T2 and get 6.312 Mbps over 96 DS0s by multiplexing four T1 lines together to form one high-speed connection.

Moving up the scale of high-speed T1 services is T3. T3 is 28 T1 lines multiplexed together for a blazing throughput of 44.736 Mbps, consisting of 672 DS0s, each of which supports 64 kbps.

Finally there’s T4. It consists of 4032 64-kbps DS0 subchannels for a whopping 274.176 Mbps of bandwidth—that’s 168 times the size of a single T1 line!

These various levels of T1 service can by implemented simulta-neously within a large enterprise network. Of course, this has the potential to become somewhat overwhelming from a management standpoint. But as long as you keep track of DS0s, you always know exactly how much bandwidth you have at your disposal.

T1’s cousin, E1, can also have multiple lines merged to provide greater throughput.